US5420742A - Degausser for tape with plural recorded segments - Google Patents

Degausser for tape with plural recorded segments Download PDF

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Publication number
US5420742A
US5420742A US08/099,619 US9961993A US5420742A US 5420742 A US5420742 A US 5420742A US 9961993 A US9961993 A US 9961993A US 5420742 A US5420742 A US 5420742A
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US
United States
Prior art keywords
tape
gap
magnet
field
magnetic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
US08/099,619
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English (en)
Inventor
Donald B. Ketcham
Robert P. McCollam
Kent R. Kalar
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
3M Co
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Minnesota Mining and Manufacturing Co
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Publication date
Application filed by Minnesota Mining and Manufacturing Co filed Critical Minnesota Mining and Manufacturing Co
Priority to US08/099,619 priority Critical patent/US5420742A/en
Assigned to MINNESOTA MINING AND MANUFACTURING COMPANY reassignment MINNESOTA MINING AND MANUFACTURING COMPANY ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KALAR, KENT R., KETCHAM, DONALD B., MCCOLLAM, ROBERT P.
Priority to PCT/US1994/006594 priority patent/WO1995004351A1/en
Priority to JP7505806A priority patent/JPH09500999A/ja
Priority to EP94921947A priority patent/EP0711445A1/en
Priority to CN94192913A priority patent/CN1128077A/zh
Priority to KR1019960700545A priority patent/KR960704308A/ko
Application granted granted Critical
Publication of US5420742A publication Critical patent/US5420742A/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
    • G11B5/024—Erasing
    • G11B5/0245—Bulk erasing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/86—Re-recording, i.e. transcribing information from one magnetisable record carrier on to one or more similar or dissimilar record carriers

Definitions

  • the present invention relates to neutralizing remanent magnetic fields in magnetic recording media. More specifically, the present invention relates to neutralizing remanent magnetization on a large scale to reduce cue tone error in contact duplication of magnetically recorded material.
  • Contact duplication involves creating an original recording, called a master, which is then placed in direct contact with a recording medium, such as a blank recording tape. Once the two media are in contact, a transfer means, such as heat or a magnetic field, is applied to the combined media, which causes the magnetically recorded signals on the master to produce a magnetic impression of one of the original signals on the recording medium.
  • a transfer means such as heat or a magnetic field
  • thermomagnetic duplication a recording medium such as chromium dioxide, chosen because of its low Curie temperature, is used as the recording medium.
  • chromium dioxide chosen because of its low Curie temperature
  • Signals also can be transferred from the master to the recording media by applying a strong magnetic field to the combination of the two contacting media.
  • a tape duplicating system which uses this signal transfer method is disclosed in U.S. Pat. No. 5,148,403.
  • tape 10 typically contains a leading length 12, followed by a segment 14 which contains a recorded program, followed by segment 16, which contains recorded signal, called a cue tone 18, followed by second recorded program 14. Additional segments and cue tones may follow.
  • the pancake is placed in a cassette loading apparatus, and a cassette, having a leader attached to a supply reel is also placed in the loading apparatus.
  • a program segment 14 is attached to the leader and is wound onto the cassette reel.
  • the loading apparatus senses the signal from the cue tone 18 following this program segment, it stops the winding, cuts the tape 10, and splices the trailing end of the tape (at the end of the segment 14) onto a length of transparent film attached to the takeup reel in the cassette being loaded.
  • a troublesome problem in some cassette loading processes is cue tone error caused by remanent magnetization in the recording tape.
  • Such remanent magnetization is typically the result of magnetic orientation fields applied to the magnetic recording medium during manufacture as disclosed, for example, in U.S. Pat. No. 2,796,359.
  • Cue tone error can lead to a condition where the tape cutting operation loses synchronization with the programs recorded on the tape, resulting in a cassette containing the end of one program followed by the beginning of another.
  • Demagnetization, or erasing, of recording tape is well known, since it is commonly done in magnetic tape recording apparatus, where magnetic tape is frequently recorded over, and it is desirable to erase the old signals prior to recording the new.
  • a direct-current, electromagnetic erase head which first subjects the medium to a saturating magnetic field of one polarity and then applies a field of reverse polarity of such magnitude to just bring the medium to zero magnetization, is disclosed in published British Patent Application No. GB 2 195 198.
  • a process for removal of remanent magnetization in the sound recording layer to reduce noise in a motion picture film strip is disclosed in U.S. Pat. No. 3,627,580.
  • a series of permanent magnets of alternating polarity, spaced at increasing distance from the medium, is used to demagnetize the magnetic recording layer by subjecting it to magnetic fields of alternating polarity and progressively diminishing strength.
  • demagnetizing devices used as part of a magnetic media manufacturing operation be of the permanent magnet type, to avoid the expense and hazard of electrical devices.
  • demagnetizing tape which will be effective against the type of cue tone error described above.
  • the inventors have diagnosed an unrecognized cause of cue tone error as being false cue tones generated by remanent magnetization in the blank recording tape used in the contact duplication process.
  • Evidence suggests that a major factor in the loss of synchronization between programs and tape loading is the manner in which the loading apparatus uses the cue tones to sense ends of programs.
  • the cue tone sensing mechanism is intended to sense cue tones 18 in segments 16 of blank tape between programs.
  • the sensor encounters a segment 16 of unrecorded tape, followed by a cue tone 18, which precisely locates the desired end of the tape and signals to the loading apparatus to stop loading and cut the tape.
  • the loading apparatus determines, based upon the length of the program being loaded, when to activate the sensing mechanism to begin looking for the next cue tone 18.
  • the inventors When there is a high level of remanent magnetization in the tape, the inventors have found that the loader senses a false cue tone almost immediately upon activation of the cue tone sensing mechanism, rather than at the point where the real cue tone occurs. The result is that loading is stopped prematurely and the tape cut, at, for example, at the location shown by 20, thereby leaving no blank tape at the end of the program.
  • Premature cutting of the tape at location 20 can cause the loading apparatus to prematurely activate the cue tone sensor for the end of the next program, which, if another false cue tone is sensed, leads to yet another premature cutting of the tape, and a cumulative error in tape length.
  • these premature tape cuttings result in programs being severely cut short, and portions of the succeeding program being added to the portion of tape which is loaded.
  • the inventors have been able to greatly reduce the cue tone error of this type by demagnetizing the recording medium before thermomagnetic duplication.
  • the added cost of commonly known tape demagnetization methods is highly burdensome in the cost-competitive market environment encountered in magnetic tape duplication.
  • the inventors have recognized that the demagnetization needed for noise reduction in tape recording is of a fundamentally different nature than that needed for reduction of cue tone error.
  • reduction of recording noise requires that remanent magnetization of the blank medium be eliminated on a small scale, namely the scale of the recorded wavelengths, which is on the order of the scale of the pigment particles. It has been found by the inventors, however, that reduction in cue tone errors only requires that large, or macro, scale remanent magnetization be reduced, and that large scale demagnetization can be achieved with a simple and cost effective process which can be applied to wide webs of recording media.
  • reduction in large scale remanent magnetization is achieved by first switching all magnetic pigment particles in the recording medium to one direction of magnetization by applying a saturating field. Then a lower strength field of opposite polarity is applied to switch the polarity direction of the magnetic particles having coercivity below the reverse field strength. The result is a large scale cancellation of fields.
  • FIG. 1 is a schematic view of a duplicated tape.
  • FIG. 2 is a schematic view of a demagnetizing slot assembly of the present invention.
  • FIG. 3 is a schematic view of another embodiment of the demagnetizing slot assembly.
  • FIG. 4 is a perspective view of another embodiment of the demagnetizing slot assembly.
  • a primary source of remanent magnetization is the magnetic field used to orient the pigment. It is quite common to find that the magnetic pigment is magnetically saturated in the orientation direction.
  • magnetic tape which is known to be magnetically saturated due to a previously applied magnetic field is magnetically neutralized by application of a demagnetizing field produced by the slot assembly 22 shown in FIG. 2.
  • two magnets 24 are oriented with like poles facing each other to define a gap 26, having a gap distance g.
  • Each magnet 24 can be mounted on a flux plate 28, as shown, and can be held on the flux plate 28 by two clamps 30. The magnets 24 tend to remain on the flux plate 28 without the clamps 30 but the clamps protect the magnets and prevent the end magnets, when a line of magnets is used as discussed below, from being pushed away from the other magnets.
  • a web such as tape 10, having been magnetically saturated in one polarity direction 32 during coating, passes through the gap 26 in a direction 34 approximately midway between the two magnets 24.
  • Flux lines 36 being in the same direction as the saturation remanent magnetization, assure that the tape 10 is in a state of magnetic saturation.
  • flux lines 38 which are in the opposite polarity direction to the saturation magnetization, partial reversal of the remanent magnetization occurs.
  • the web direction 34 and the charge direction 32 are opposite each other and the north poles of the magnets 24 face each other.
  • the web direction 34 and the charge direction 32 can be the same with the south poles of the magnets 24 facing each other.
  • the strength of the neutralizing field represented by flux lines 38 is equal to or slightly less than the intrinsic coercivity of the magnetic medium, the remanent magnetization of the medium will be very near to zero, as measured by a vibrating sample magnetometer, or VSM.
  • the magnetic pigment is chromium dioxide, a pigment commonly used in thermomagnetic duplication, the magnetic field strength should range from 600-800 Gauss, although other strengths also could be used. For one family of chromium dioxide pigments, a magnetic field strength of about 714 Gauss has been found suitable.
  • the strength of the field in the gap 26, represented by the flux lines 36, 38, can be adjusted by adjusting the gap height g, which reduces the field strength. If only one magnet 24 were to be used in this embodiment, the magnetic field would be of similar shape, and, at least in principle, the demagnetizer should function in a similar manner, although additional vertical components of magnetization could remain on the tape. Using two magnets, however, provides a stronger magnetic field, due to superposition of two fields, and also reduces the variation in field strength across the gap distance g, thereby making the device more tolerant of tape movement between the magnets 24 during operation.
  • the field strength is also enhanced by the flux plates 28, which can be made of a soft magnetic material, such as steel, and which hold the side clamps 30, which can be made of a nonmagnetic material such as aluminum.
  • Each magnet 24, flux plate 28, and pair of clamps 30 form a magnet assembly. The two magnet assemblies are held in place relative to each other to form a single slot assembly 22 by clamping or other known holding methods.
  • this slot assembly 22 can be oriented relative to the orientation field of the coating apparatus, so that the orientation 32 of the tape 10 is in the same direction as flux lines 36 as the tape 10 enters the slot assembly 22, thereby assuring that the flux lines 38 will run in the opposite direction as the tape 10 leaves the slot assembly 22 to produce the desired neutralization of remanent magnetization.
  • This is accomplished when the web direction 34 and the charge direction 32 are opposite each other and the north poles of the magnets 24 face each other.
  • this is accomplished when the web direction 34 and the charge direction 32 are the same with the south poles of the magnets 24 facing each other.
  • the need for proper orientation of the demagnetizer can lead to error in use, since those who install the demagnetizer may not fully appreciate its principle of operation. This, and other improvements, can be achieved by the embodiment shown in FIG. 3.
  • the slot assembly 40 provides its own saturation field before applying the neutralization field. This makes it independent of the direction of any previously applied magnetic fields, such as an orientation field applied during coating.
  • two magnets 42, 44 are placed side by side, with opposite poles facing the gap 26, and with the pole faces of the magnets evenly aligned to define pole planes 46, which, in turn, define the gap 26.
  • the pole planes 46 are perpendicular to the plane of the figure. The apparatus would work with the pole faces of the magnets not planar, but some flux lines would be skewed.
  • the magnetic field within the gap 26 is the result of the interaction of the fields of the four magnets contained in magnet assemblies.
  • the tape 10 As the tape 10 enters the gap 26 travelling in direction 34, it first encounters the field represented by flux lines 48 (such as 714 G), followed by the much stronger flux lines 50 (such as 2400 G), produced by the combination of magnets 42, 44, which saturate the tape 10 in a first direction.
  • the flux lines 48 are in the opposite direction to the saturation magnetization, the flux lines 50 will saturate the tape 10.
  • a weaker field 52 such as 714 G
  • the gap distance g By adjusting the gap distance g, the strength of the magnetic fields to which the tape 10 is subjected can be adjusted, with an increase causing a decrease in field strength.
  • the critical adjustment is, of course, the final field strength, represented by flux lines 52. This adjustment can be made by testing samples of magnetic media using a VSM, and adjusting the gap distance g to obtain the minimum remanent magnetization.
  • FIGS. 2 and 3 could be made with only the magnets shown, the inventors have found that an additional difficulty is encountered when these embodiments are used on wide webs. This difficulty is that very wide permanent magnets are not readily available at a reasonable cost. Therefore, the configuration shown in FIG. 4 has been devised.
  • a magnet assembly 54 includes several smaller magnets 56, 58, which are placed in rows and held in place by a flux plate 60 and clamps 62. Only one magnet assembly is shown.
  • the magnetic field strength can be made significantly more uniform in the crossweb direction 64 if iron or other soft magnetic shims 66 are placed across the faces of magnets 56, 58 in areas of high field strength, to shunt part of the magnetic flux away from the gap.
  • Magnets 56, 58, along with the clamps 62 and the steel flux plate 60, can be held together by adhesive or other known fasteners. Magnet assemblies can be held in their proper positions with respect to each other by holding or clamping devices known in the art.
  • the demagnetizer of FIG. 4 has been used to neutralize thermomagnetic recording media to a remanent magnetization level of less than 5% of saturation. This was found to be well below the level needed for reducing cue tone errors to an acceptable level in a commercially available cassette loading apparatus.

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  • Manufacturing Of Magnetic Record Carriers (AREA)
US08/099,619 1993-07-30 1993-07-30 Degausser for tape with plural recorded segments Expired - Fee Related US5420742A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
US08/099,619 US5420742A (en) 1993-07-30 1993-07-30 Degausser for tape with plural recorded segments
PCT/US1994/006594 WO1995004351A1 (en) 1993-07-30 1994-06-10 Contact duplication tape degausser
JP7505806A JPH09500999A (ja) 1993-07-30 1994-06-10 接触複写テープ消磁装置
EP94921947A EP0711445A1 (en) 1993-07-30 1994-06-10 Contact duplication tape degausser
CN94192913A CN1128077A (zh) 1993-07-30 1994-06-10 接触复制磁带去磁器
KR1019960700545A KR960704308A (ko) 1993-07-30 1994-06-10 접촉 복제 테이프 소자기(contact duplication tape degausser)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US08/099,619 US5420742A (en) 1993-07-30 1993-07-30 Degausser for tape with plural recorded segments

Publications (1)

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US5420742A true US5420742A (en) 1995-05-30

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Application Number Title Priority Date Filing Date
US08/099,619 Expired - Fee Related US5420742A (en) 1993-07-30 1993-07-30 Degausser for tape with plural recorded segments

Country Status (6)

Country Link
US (1) US5420742A (ko)
EP (1) EP0711445A1 (ko)
JP (1) JPH09500999A (ko)
KR (1) KR960704308A (ko)
CN (1) CN1128077A (ko)
WO (1) WO1995004351A1 (ko)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6714398B2 (en) * 2002-06-07 2004-03-30 Data Security, Inc. Bulk degausser with fixed arrays of magnetic poles configured for thick and small form factor, high coercivity media
US20060018075A1 (en) * 2004-07-23 2006-01-26 Data Security, Inc. Permanent magnet bulk degausser
US20080013245A1 (en) * 2006-07-14 2008-01-17 Schultz Robert A Method and Reciprocating Apparatus for Permanent Magnet Erasure of Magnetic Storage Media
US20080013244A1 (en) * 2006-07-14 2008-01-17 Schultz Robert A Method and Apparatus for Permanent Magnet Erasure of Magnetic Storage Media
US20100246057A1 (en) * 2009-03-31 2010-09-30 Sun Microsystems, Inc. Servo writer providing a pre-writing, longitudinal magnetic bias in a magnetically unoriented tape supply
US20140191035A1 (en) * 2011-08-10 2014-07-10 Giesecke & Devrient Gmbh Checking Arrangement for Value-Document Check

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996023302A1 (en) * 1995-01-23 1996-08-01 Minnesota Mining And Manufacturing Company Degausser for tape used with contact duplication
DE10013507A1 (de) 2000-03-20 2001-09-27 Basf Ag Chirale 1,3-Dioxanverbindungen
JP7249295B2 (ja) * 2020-01-10 2023-03-30 株式会社ニフコ シートカバーの取付構造

Citations (11)

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US2526358A (en) * 1946-10-18 1950-10-17 Indiana Steel Products Co Demagnetizing device
US2535498A (en) * 1947-11-07 1950-12-26 Brush Dev Co Erasing head and apparatus for magnetic recorders
US2796359A (en) * 1952-07-05 1957-06-18 Audio Devices Inc Production of magnetic sound recording tape
US3627580A (en) * 1969-02-24 1971-12-14 Eastman Kodak Co Manufacture of magnetically sensitized webs
US4003336A (en) * 1974-08-27 1977-01-18 Basf Aktiengesellschaft Device for the magnetic orientation of magnetic recording media
US4631602A (en) * 1982-12-13 1986-12-23 E. I. Du Pont De Nemours And Company Process for thermoremanent duplication of magnetic tapes using transverse laser beams spanning the tape width
US4703230A (en) * 1985-08-30 1987-10-27 Kabushiki Kaisha Toshiba Raster operation circuit
GB2195198A (en) * 1986-09-17 1988-03-30 Racal Recorders Ltd Erasing head
US4897759A (en) * 1986-11-19 1990-01-30 Garner Industries, Inc. Method and apparatus for erasing information from magnetic material
US5148403A (en) * 1987-01-29 1992-09-15 Sony Magnescale, Inc. Production of prerecorded tape cassettes
US5204801A (en) * 1992-04-17 1993-04-20 Garner Industries, Inc. Degaussing technique

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DE2261450B2 (de) * 1972-12-15 1977-08-25 Agfa-Gevaert Ag, 5090 Leverkusen Loescheinrichtung fuer bewegte magnetische aufzeichnungstraeger
DE3010873A1 (de) * 1980-03-21 1981-10-01 Basf Ag, 6700 Ludwigshafen Magnetisierungseinrichtung zur erzeugung einer magnetischen vorzugsrichtung in magnetischen aufzeichnungstraegern
DE3736024C1 (en) * 1987-10-24 1989-03-23 Agfa Gevaert Ag Demagnetising device
US5132860A (en) * 1989-10-13 1992-07-21 Von Stein Paul W Magnetic media erasure system
GB2239976B (en) * 1989-12-20 1993-12-22 Toshiba Emi Kk Method of inspecting pancake tape

Patent Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2526358A (en) * 1946-10-18 1950-10-17 Indiana Steel Products Co Demagnetizing device
US2535498A (en) * 1947-11-07 1950-12-26 Brush Dev Co Erasing head and apparatus for magnetic recorders
US2796359A (en) * 1952-07-05 1957-06-18 Audio Devices Inc Production of magnetic sound recording tape
US3627580A (en) * 1969-02-24 1971-12-14 Eastman Kodak Co Manufacture of magnetically sensitized webs
US4003336A (en) * 1974-08-27 1977-01-18 Basf Aktiengesellschaft Device for the magnetic orientation of magnetic recording media
US4631602A (en) * 1982-12-13 1986-12-23 E. I. Du Pont De Nemours And Company Process for thermoremanent duplication of magnetic tapes using transverse laser beams spanning the tape width
US4703230A (en) * 1985-08-30 1987-10-27 Kabushiki Kaisha Toshiba Raster operation circuit
GB2195198A (en) * 1986-09-17 1988-03-30 Racal Recorders Ltd Erasing head
US4897759A (en) * 1986-11-19 1990-01-30 Garner Industries, Inc. Method and apparatus for erasing information from magnetic material
US5148403A (en) * 1987-01-29 1992-09-15 Sony Magnescale, Inc. Production of prerecorded tape cassettes
US5204801A (en) * 1992-04-17 1993-04-20 Garner Industries, Inc. Degaussing technique

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6714398B2 (en) * 2002-06-07 2004-03-30 Data Security, Inc. Bulk degausser with fixed arrays of magnetic poles configured for thick and small form factor, high coercivity media
US20060018075A1 (en) * 2004-07-23 2006-01-26 Data Security, Inc. Permanent magnet bulk degausser
US20080180203A1 (en) * 2004-07-23 2008-07-31 Data Security, Inc. Permanent magnet bulk degausser
US7593210B2 (en) 2004-07-23 2009-09-22 Data Security, Inc. Permanent magnet bulk degausser
US20080013245A1 (en) * 2006-07-14 2008-01-17 Schultz Robert A Method and Reciprocating Apparatus for Permanent Magnet Erasure of Magnetic Storage Media
US20080013244A1 (en) * 2006-07-14 2008-01-17 Schultz Robert A Method and Apparatus for Permanent Magnet Erasure of Magnetic Storage Media
US7701656B2 (en) 2006-07-14 2010-04-20 Data Security, Inc. Method and apparatus for permanent magnet erasure of magnetic storage media
US7715166B2 (en) 2006-07-14 2010-05-11 Data Security, Inc. Method and reciprocating apparatus for permanent magnet erasure of magnetic storage media
US20100246057A1 (en) * 2009-03-31 2010-09-30 Sun Microsystems, Inc. Servo writer providing a pre-writing, longitudinal magnetic bias in a magnetically unoriented tape supply
US7986485B2 (en) * 2009-03-31 2011-07-26 Oracle America, Inc. Servo writer providing a pre-writing, longitudinal magnetic bias in a magnetically unoriented tape supply
US20140191035A1 (en) * 2011-08-10 2014-07-10 Giesecke & Devrient Gmbh Checking Arrangement for Value-Document Check
US9183421B2 (en) * 2011-08-10 2015-11-10 Giesecke & Devrient Gmbh Checking arrangement for value-document check

Also Published As

Publication number Publication date
WO1995004351A1 (en) 1995-02-09
JPH09500999A (ja) 1997-01-28
EP0711445A1 (en) 1996-05-15
CN1128077A (zh) 1996-07-31
KR960704308A (ko) 1996-08-31

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Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:KETCHAM, DONALD B.;MCCOLLAM, ROBERT P.;KALAR, KENT R.;REEL/FRAME:006710/0855

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